Fluorine-Containing Elastomer and Composition Thereof

ABSTRACT

A fluorine-containing elastomer having a copolymer composition, which comprises (a) 50-85 mol. % of vinylidene fluoride, (b) 0-25 mol. % of tetrafluoroethylene, (c) 7-20 mol. % of perfluoro(methyl vinyl ether), (d) 2.5-15 mol. % of CF 2 ═CFO[CF 2 CF(CF 3 )O]nCF 3  (n: 2-6), (e) 0.1-2 mol. % of CF 2 ═CFO[CF 2 CF(CF 3 )O]mCF 2 CF 3  (m: 2-6), and (f) 0.1-2 mol. % of RfX (Rf: an unsaturated fluorohydrocarbon group having 2-8 carbon atoms, which can contain at least one ether bond, X: bromine or iodine), can provide a fluorine-containing elastomer composition, which comprises 100 parts by weight of the fluorine-containing elastomer, 0.1-10 parts by weight of an organic peroxide, 0.1-10 parts by weight of a polyfunctional unsaturated compound, and at least 2 parts by weight of an acid acceptor. The composition can give vulcanizates having a distinguished elongation at break at high temperatures such as 100° C., and distinguished compression set characteristics at low temperatures such as 0° C.

TECHNICAL FIELD

The present invention relates to a fluorine-containing elastomer and acomposition thereof, and more particularly to a fluorine-containingelastomer capable of giving vulcanizates with distinguished moldingprocessability, low-temperature characteristics, and solvent resistance,and a composition thereof.

BACKGROUND ART

Fluorine-containing elastomers comprising vinylidenefluoride-tetrafluoroethylene-perfluoro(methyl vinyl ether) as the mainstructural unit have not only distinguished heat resistance and solventresistance peculiar to the fluorine-containing elastomer, but also havegood low-temperature characteristics, and thus have been so far used inmany industrial fields including the automobile industry. However, eventhe fluorine-containing elastomers often fails to satisfy the recenttechnical progress, where particularly more strict requirements for thelow-temperature characteristics and resistance to alcoholic solventssuch as methanol, etc. are imposed. Due to the recent exhaust gasregulations, etc., further requirements for the heat resistance, solventresistance, and low-temperature characteristics have been also imposedon the fluorine-containing elastomers.

To solve the problems, it has been so far proposed to prepare thefluorine-containing elastomer by copolymerizing a monomer having aplurality of ether bonds on the side chains in place of perfluoro(methylvinyl ether), where the monomer must be copolymerized in a highproportion to obtain copolymers in an elastomeric state, whereas in alow proportion only semi-resinous state copolymers will be obtained,resulting in deterioration of the low-temperature characteristics.Actually, 12-50% by mole is recommended for the copolymerizationproportion of the monomer, and all of Examples in the followingreference teach copolymerization proportions of 25-32% by mole. However,such fluorine-containing elastomer containing the monomer in a highproportion shows a poor mechanical strength and moreover has such aproblem as a poor molding processability, e.g. easy occurrence offoaming at the time of molding.

Patent Literature 1: JP-B-5-13961

Perfect fuel oil resistance is required for automobile fuel sealmaterials, and thus commercially available fluororubber is now usedmainly for this purpose. Besides the ordinary gasoline,oxygen-containing fuels such as ether, alcohol, etc. have been now usedas automobile fuels from the viewpoint of combustion efficiency, etc.Fluororubber having an increased fluorine content can respond to theoxygen-containing fuel, but the increased fluorine content candeteriorate the cold resistance, giving rise to fear of fuel leakage inwinter cold districts, whereas a decreased fluorine content can improvethe cold resistance, but can lose the resistance to theoxygen-containing fuel. It is now very hard to satisfy these tworequirements at the same time.

DISCLOSURE OF THE INVENTION

Problem to be Solved by the Invention

The present applicants previously proposed a fluorine-containingelastomer capable of giving vulcanizates having distinguishedlow-temperature characteristics and solvent resistance, withoutdeteriorating the molding processability and compression setcharacteristics originally possessed by the fluorine-containingelastomer, which comprises:

(a) vinylidene fluoride 50-85 mol. %  (b) tetrafluoroethylene 0-25 mol.% (c) perfluoro(methyl vinyl ether) 7-20 mol. % (d)CF₂═CFO[CF₂CF(CF₃)O]nCF₃ 3-15 mol. % (where n is an integer of 2-6) (e)RfX (where Rf is an unsaturated fluorohydro- 0.1-2 mol. %  carbon grouphaving 2-8 carbon atoms, which can contain at least one ether bond, andX is bromine or iodine)

Patent Literature 2: JP-A-2004-346087

The proposed fluorine-containing elastomer can satisfy theafore-mentioned desired characteristics, and can show a moredistinguished low-temperature characteristics particularly when n is aninteger of 4-6 in Component (d), than that when n is an integer of 2-3,so long as the copolymerization proportion is the same, and also cangive equivalent low-temperature characteristics even in a lowercopolymerization proportion.

The vulcanizates of the proposed fluorine-containing elastomer havingsuch characteristics can be effectively used as automobile fuel sealmaterials, etc. In view of such situations that engine room insides areexposed to low temperatures in an engine stop state in cold districts,whereas to high temperatures in an engine driving state,ultracold-resistant fluorine-containing elastomers are still moredesired to withstand such severe use circumstances.

An object of the present invention is to provide a fluorine-containingelastomer capable of giving vulcanizates having a distinguishedelongation at break at high temperatures such as 100° C., anddistinguished compression set characteristics at low temperatures suchas 0° C., and a composition thereof.

Means for Solving the Problem

The object of the present invention can be attained by afluorine-containing elastomer, which comprises:

(a) vinylidene fluoride 50-85 mol. %  (b) tetrafluoroethylene 0-25 mol.% (c) perfluoro(methyl vinyl ether) 7-20 mol. % (d)CF₂═CFO[CF₂CF(CF₃)O]nCF₃ 2.5-15 mol. %   (where n is an integer of 2-6)(e) CF₂═CFO[CF₂CF(CF₃)O]mCF₂CF₃ 0.1-2 mol. %  (where m is an integer of2-6) (f) RfX (where Rf is an unsaturated fluorocarbon 0.1-2 mol. % group having 2-8 carbon atoms, which can contain at least one etherbond, and X is bromine or iodine)The fluorine-containing elastomer can be obtained by copolymerizationpreferably in the presence of a bromine- and/or iodine-containingcompound, represented by the general formula R(Br)n(I)m (where R is asaturated fluorohydrocarbon group or a saturated chlorofluorohydrocarbongroup, each having 2-6 carbon atoms, and n and m are each 0, 1 or 2, andm+n is 2).

The fluorine-containing elastomer can provide a fluorine-containingelastomer composition by addition of 0.1-10 parts by weight of anorganic peroxide, 0.1-10 parts by weight of a polyfunctional unsaturatedcompound, and at least 2 parts by weight of an acid acceptor to 100parts by weight of the fluorine-containing elastomer.

EFFECT OF THE INVENTION

The present fluorine-containing elastomer can give vulcanizates havingdistinguished low-temperature characteristics (glass transitiontemperature) and solvent resistance (methanol resistance) in addition tothe heat resistance, molding processability, and compression setcharacteristics, originally possessed by the fluorine-containingelastomer, and thus can be effectively used as molding materials for Orings, oil seals, fuel hoses, etc.

Particularly, the peroxide-crosslinked fluorine-containing elastomer hasa distinguished elongation at break at high temperatures such as 100° C.and distinguished compression set characteristics at low temperaturessuch as 0° C., and thus can be effectively used as automobile fuel sealmaterials capable of withstanding use in cold districts, morespecifically severe use circumstances such that the engine room insideis exposed to low temperatures in an engine stop state in colddistricts, whereas to high temperatures in an engine driving state.

BEST MODES FOR CARRYING OUT THE INVENTION

The present fluorine-containing elastomer has such copolymer compositionproportions as (a) 50-85 mol. %, preferably 60-85 mol. %, of vinylidenefluoride, (b) 0-25 mol. %, preferably 0-20 mol. %, oftetrafluoroethylene, (c) 7-20 mol. %, preferably 7-15 mol. %, ofperfluoro(methyl vinyl ether), (d) 2.5-15 mol. %, preferably 3-10 mol.%, of CF₃-terminated perfluoro vinyl ether, represented by theafore-mentioned general formula, (e) 0.1-2 mol. %, preferably 0.5-1 mol.%, of CF₂CF₃-terminated perfluoro vinyl ether, represented by theafore-mentioned general formula, and (f) 0.1-2 mol. %, preferably0.3-1.5 mol. %, of a bromine- or iodine-containing unsaturated compound,represented by the aforementioned general formula, where the compositionproportions are selected in ranges capable of giving vulcanizates havingdesired low-temperature characteristics and solvent resistance. When thecopolymer composition proportion of component (e) is less than 0.1 mol.%, the desired cold resistance can not be attained, whereas whencopolymerized in a proportion of more than 2 mol. %, the elongation atbreak at high temperature will be lowered.

Vinylidene fluoride of Component (a) is copolymerized with each of thefollowing Components (b)-(f).

Further copolymerization of tetrafluoroethylene of Component (b) canremarkably improve the solvent resistance, where the low-temperaturecharacteristics will be deteriorated in too high a copolymer compositionproportion, and thus to proportion of 25 mol. % or less, preferably 20mol. % or less can be recommended. Copolymerization of Component (b) canalso remarkably improve the resistance to fuels mixed with anoxygen-containing compound, such as methanol-gasoline mixed fuel,ethanol-gasoline mixed fuel, etc., and alcoholic fuel such as methanol,ethanol, etc.

Perfluoro(methyl vinyl ether) of Component (c) can give a flexibility tothe resulting copolymer, and is also an essential component forimproving the low-temperature characteristics, particularly TR₇₀ valuesin the TR test.

CF₃-terminated perfluoro vinyl ether of Component (d) for use herein canbe a single component selected from the compounds represented by thegeneral formula, or a mixture of at least two compounds having various nvalues. As similar perfluoro vinyl ethers thereto, compounds representedby the following general formula are known:

CF₂═CFO [CF₂CF(CF₃)O] pRf

(where Rf: perfluoroalkyl groups of C₁-C₃, and p: an integer of 1-3).Copolymerization of a monomer having a perfluoropropyl group as deemedto be particularly preferable Rf group can give the low-temperaturecharacteristics, though lowering of molecular weight, lowering ofmolding processability such as occurrence of foaming, etc. at the timeof molding, lowering of mechanical strength, etc. are encountered. Sucha compound can be copolymerized within such a range as not todeteriorate the desired properties, for example, in a proportion of 1mol. % or less.

Patent Literature 3: JP-A-2002-37813

CF₃-terminated perfluoro vinyl ether of Component (d), represented bythe afore-mentioned general formula, can be obtained by reaction ofCF₃OCF(CF₃)COF with hexafluoropropene oxide in the presence of a cesiumfluoride catalyst, a diglyme solvent, etc., followed by reaction withanhydrous potassium carbonate, and by thermal decomposition reaction,where the product is a mixture of n=2-6, but individual perfluorovinylethers having various n values can be separated from one another byfractional distillation, and can be used as single compounds.Particularly, n=4-6 is preferable from the viewpoint of low-temperaturecharacteristics. Or the mixture can be also used, as such withoutfractional distillation.

CF₂CF₃-terminated perfluoro vinyl ether of Component (e) for use hereinis a single component selected from the compounds, represented by theafore-mentioned general formula, or can be a mixture of at least twocompounds having various n values. Such a perfluoro vinyl ether can beobtained by reaction of CF₃CF₂OCF(CF₃)COF with hexafluoropropene oxidein the presence of a cesium fluoride catalyst, a diglyme solvent, etc.,followed by reaction with anhydrous potassium carbonate, and by thermaldecomposition reaction, where the product is a mixture of n=2-6, butindividual perfluoro vinyl ethers having various n values can beseparated from one another by fractional distillation, and can be usedas single compounds. Particularly, n=4-6 is preferable from theviewpoint of low-temperature characteristics. Or the mixture can be alsoused as such without fractional distillation.

Bromine- or iodine-containing compound of Component (f) for use hereinincludes, for example, CF₂═CFOCF₂CF₂Br, CF₂═CFOCF₂CF(CF₃)OCF₂CF₂Br,CF₂═CFBr, CF₂═CHBr, CF₂=CFI, CF₂═CHI, etc., where the Rf group is anunsaturated fluorohydrocarbon group having 2-8 carbon atoms, which cancontain at least one ether bond (see the following Patent Literature 4).CF₂═CFOCF₂CF₂Br, CF₂═CFI, and CF₂═CHI can be preferably used.

To adjust the molecular weight of the present fluorine-containingelastomer copolymer, or to improve the molding processability,particularly to suppress occurrence of foaming at the time of curingstep, it is very effective to conduct the copolymerization reaction inthe presence of a bromine- and/or iodine-containing compound,represented by the following general formula:

R(Br)n(I)m

Patent Literature 4: JP-B-54-1585

Such compounds include, for example, ICF₂CF₂CF₂CF₂I, ICF₂CF₂CF₂CF₂Br,ICF₂CF₂Br, etc., and ICF₂CF₂CF₂CF₂I, is particularly preferable from theviewpoint of curing characteristics, etc. Other examples are disclosedin the following Patent Literatures 5 and 6.

Patent Literature 5: JP-B-63-308008

Patent Literature 6: JP-B-58-4728

Such compounds act as a chain transfer agent to adjust the molecularweights of the resulting copolymers. As a result of the chain transferreaction, copolymers having a bromine atom and/or an iodine atom bondedto the molecule terminal can be obtained, with the result that thebonded sites act as curing sites at the time of vulcanization moldingstep. However, when such compounds are used in a larger proportion, themechanical properties of the ultimate molding products will be lowered.Thus, the recommended proportion is about 1 wt. % or less, preferablyabout 0.5 to about 0.01 wt. %, on the basis of the weight of totalmonomers.

To improve the compression set characteristics of the vulcanizationmolding products, the following perfluoro divinyl ether can becopolymerized in a proportion of about 1 wt. % or less, preferably about0.5 to about 0.1 wt. % on the basis of the weight of total monomers fromthe viewpoint of the mechanical properties of the molding products:

CF₂═CFOCF₂CF(CF₃)OCF₂CF₂OCF═CF₂

Other monomers, for example, fluorine-containing monomers such astrifluoroethylene, hexafluoropropene, chlorotrifluoroethylene, etc. canbe further polymerized in such a range as not to deteriorate the desiredproperties of the present fluorine-containing elastomer.

The present fluorine-containing elastomer can be prepared by an aqueousemulsion polymerization process or by an aqueous suspensionpolymerization process. The aqueous emulsion polymerization process canuse a reaction initiator system based on either single water-solubleperoxide or a redox system of a water-soluble peroxide and awater-soluble reducing compound. The water-soluble peroxide for useherein includes, for example, ammonium persulfate, potassium persulfate,sodium persulfate, etc., whereas the water-soluble reducing compound foruse herein includes, for example, sodium sulfite, sodium hydrogensulfite, etc. As a stabilizer for the aqueous emulsion, a pH-adjustingagent (buffer), such as sodium monohydrogen phosphate, sodium dihydrogenphosphate, potassium monohydrogen phosphate, potassium dihydrogenphosphate, etc. can be used.

An emulsifier for use in the emulsion polymerization process includes,generally, a fluorinated carboxylate (see the afore-mentioned PatentLiterature 1), preferably the following compound:

CF₃CF₂CF₂O[CF(CF₃)CF₂O]nCF(CF₃)COONH₄

-   -   n: 1 or 2        The emulsifier can be used as an aqueous solution containing        about 1 to about 30 wt. %, preferably about 5 to about 20 wt. %,        thereof. When the amount of the emulsifier is less than about 1        wt. %, monomers and the resulting copolymers can not be        uniformly dispersed in the aqueous medium, whereas too large an        amount thereof will make the process economically        disadvantageous.

Copolymerization reaction is carried out at a temperature of about 20°to about 80° C., preferably about 25° to about 60° C. Too high apolymerization temperature will give rise to such problems as occurrenceof foaming at the time of molding processing and deterioration ofcompression set characteristics of vulcanization molding products.Polymerization pressure for use herein is generally about 5 MPa or less.

The resulting fluorine-containing elastomer has a glass transitiontemperature Tg of −30° to −45° C. The molecular weight of the resultingcopolymer is not particularly limited, but it is desirable that thenumber average molecular weight Mn (GPC method; tetrahydrofuran solvent)is about 10,000 to about 1,000,000, preferably about 50,000 to about300,000. Desirably, solution viscosity ηsp/c (35C, 1 wt. % methyl ethylketone solution) as an index of molecular weight is about 0.1 to about 2dl/g, preferably about 0.2 to about 1 dl/g.

The present fluorine-containing elastomer having such properties can becured by so far well-known various vulcanization processes, such as aperoxide vulcanization process, a polyamine vulcanization process, andpolyol vulcanization process, or an irradiation process by radiationrays, electron beams, etc., preferably the peroxide vulcanizationprocess using an organic peroxide can provide vulcanizates havingdistinguished mechanical strength and forming carbon-carbon bonds in astable cross-linking structure, resulting in distinguished chemicalresistance, abrasion resistance, solvent resistance, etc.

Organic peroxide for use in the peroxide vulcanization process includes,for example, 2,5-dimethyl-2,5-bis(t-butylperoxy)hexane,2,5-dimethyl-2,5-bis(t-butylperoxy)hexine-3, benzoyl peroxide,bis(2,4-dichlorobenzoyl)peroxide, dicumyl peroxide, di-t-butyl peroxide,t-butyl cumyl peroxide, t-butylperoxybenzene,1,1-bis(t-butylperoxy)-3,5,5-trimethylcyclohexane,2,5-dimethylhexane-2,5-dihydroxyperoxide,α,α′-bis(t-butylperoxy)-p-diisopropylbenzene,2,5-dimethyl-2,5-di(benzylperoxy)hexane, t-butylperoxyisopropylcarbonate, etc.

In the peroxide vulcanization process using such organic peroxides, itis preferable to use a polyfunctional unsaturated compound as acocrosslinking agent at the same time, such as tri(meth)allylisocyanurate, tri(meth)allyl cyanurate, triallyl trimellitate,N,N′-m-phenylene bismaleimide, diallyl phthalate,tris(diallylamine)-s-triazine, triallyl phosphite, 1,2-polybutadiene,ethylene glycol diacrylate, diethylene glycol diacrylate, etc. Bysimultaneous use of the cocross-linking agent, vulcanizates having muchmore distinguished vulcanization characteristics, mechanical strength,compression set characteristics, etc. can be obtained.

Furthermore, hydrotalcite, oxides or hydroxides of divalent metals, suchas oxides or hydroxides of calcium, magnesium, lead, zinc, etc. can bealso used as acid acceptor.

The foregoing components are added to the peroxide vulcanization systemin the following proportions on the basis of 100 parts by weight of thepresent fluorine-containing elastomer: about 0.1 to about 10 parts byweight, preferably about 0.5 to about 5 parts by weight, of an organicperoxide, about 0.1 to about 10 parts by weight, preferably about 0.5 toabout 5 parts by weight, of a cocross-linking agent, if required, andfurthermore at least about 2 parts by weight, preferably about 3 toabout 20 parts by weight, of an acid acceptor. When the acid acceptor isused in a proportion of less than about 2 parts by weight, the corrosionresistance to metals will be deteriorated.

For the vulcanization, so far well known fillers, reinforcing agents,plasiticizers, lubricants, processing aids, pigments, etc. can beappropriately added thereto, besides the afore-mentioned components.Carbon black as a filler or a reinforcing agent can be used generally ina proportion of about 10 to about 50 parts by weight on the basis of 100parts by weight of the present fluorine-containing elastomer.

Addition of fine bituminous powders can improve the compression setcharacteristics and can contribute to elongation of the life of sealmaterials, etc. due to the improvement of heat resistance, whereasaddition of a flat filler can improve the fuel oil blockability,contributing to more strict prevention of automobile fuel, etc. as asealing target from transpiration.

As fine bituminous powders, those obtained by pulverizing bituminousmaterials such as coal, etc. to fine powers having an average particlesize of about 10 μm or less, generally about 1 to about 10 μm,preferably about 3 to about 8 μm, can be used. Above an average particlesize of about 10 μm, the strength at break or elongation at break ofrubber will be lowered, resulting in deterioration of practicalstrength. Actually, commercially available products such as MineralBlack 325BA of Keystone Filler & Mfg. Co., etc. can be used as such. Thefine bituminous powders can be used in a proportion of about 40 parts byweight or less, preferably about 5 to about 30 parts by weight, on thebasis of 100 parts by weight of the present fluorine-containingelastomer. Above about 40 parts by weight the viscosity of the resultingcomposition will be too high, giving rise to troubles at the time ofkneading or molding.

The flat filler for use herein is at least one of clay, mica, graphite,molybdenum disulfide, etc. which have an average particle size of about0.5 to about 50 μm, preferably about 5 to about 30 μm, and an aspectratio of 3 or more, preferably 5-30. When the average particle size isless than about 0.5 μm, or the aspect ratio is less than 3, the fuelblockability is no more improved, whereas the average particle size ismore than about 50 μm, the strength at break or elongation at break ofrubber will be lowered, resulting in deterioration of practicalstrength. The flat filler can be used in a proportion of about 40 partsby weight or less, preferably about 5 to about 30 parts by weight, onthe basis of 100 parts by weight of the present fluorine-containingelastomer. Above 40 parts by weight the viscosity of the resultingcomposition will be increased, resulting in failure of kneading, anddeterioration of sealability due to much higher hardness of cross-linkedseal materials.

The afore-mentioned components are kneaded by ordinary mixing methods,for example, by roll mixing, kneader mixing, Banbury mixing, solutionmixing, etc., and the kneaded products are vulcanized generally by pressvulcanization at about 100° to about 250° C. for about 1 to about 60minutes, and preferably furthermore by oven vulcanization (secondaryvulcanization) at about 150° to about 250° C. within about 30 hours.

By the organic peroxide cross-linking, the present fluorine-containingelastomer can give vulcanizates having the following low-temperaturecharacteristics:

−43° C.≦TR₁₀<−30° C.<TR₇₀≦−20° C.

where TR₁₀ and TR₇₀ values show temperatures for 10% or 70% recoveries,from the initial elongation, respectively, when samples are elongated by50% in TR tests, vitrificated by lowering the temperature to less thanglass transition temperature Tg, and strain-relaxed by graduallyincreasing the temperature.

To satisfy the conditions for the TR₁₀ and TR₇₀ values it is desirableto make sum total in combination of perfluoro(methyl vinyl ether) ofComponent (c) with perfluoro vinyl ethers of Components (d) and (e) to10 mol. % or more, preferably 15 mol. % or more, more preferably 15-37mol. %. When the sum total in the combination is less than 10 mol. %,the resulting copolymer will be brought into a semi-resinous state orthe low-temperature characteristics, particularly TR₇₀ value, will bedeteriorated.

Examples

The present invention will be described in detail below, referring toExamples.

Reference Example 1

36 g of cesium fluoride, 360 g of diglyme, and 4.18 kg of CF₃OCF(CF₃)COFwere charged into a stainless steel autoclave having a capacity of 10 L,provided with a stirrer, stirred overnight, and then cooled to −10° C.,and 12.0 kg of hexafluoropropene oxide was added thereto at a feed rateof 150 g/hr. After the end of addition, the mixture was further stirredfor 2 hours, while keeping that temperature, and then returned to roomtemperature. Then, stirring was discontinued, and the mixture wasallowed to stand. Then, only the fluorocarbon phase was carefullywithdrawn from the lower outlet of the autoclave. 15.9 kg of thefluorocarbon phase thus obtained was analyzed by gas chromatography(GC), and found to have the following composition:

CF₃O[CF(CF₃)CF₂O]nCF(CF₃)COF n GC (%) 2 1 3 27 4 50 5 20 6 2

1.2 kg of the resulting fluorocarbon phase and 1.2 kg of anhydrouspotassium carbonate were charged into a glass reactor vessel having acapacity of 10 L, provided with a stirrer, and heated to 130° C. Aftercompletion of carbon dioxide gas generation, the vessel inside pressurewas reduced to 1 Torr to recover unreacted fluorocarbon mixture and avery small amount of diglyme (total: 30 g). Then, the vessel insidepressure was returned to the normal pressure, and reaction was conductedat 200°-270° C. for 10 hours to obtain the following compounds. Theresulting liquid was recovered by a cold trap. 1.0 kg of the resultingproduct was analyzed by GC and found to have the following composition.Vinylation reaction proceeded substantially quantitatively (90% ormore), and thus the composition was not changed substantially before andafter the reaction.

CF₂═CFO[CF₂CF(CF₃)O]nCF₃ n GC (%) 2 1 3 27 4 50 5 20 6 2

The resulting vinyl ether compounds were distilled to isolate theindividual compounds having the respective n values from one another.The individual compounds were identified by ¹⁹F-NMR (chemical shift wasbased on CFCl₃).

(n = 2)MPr₂VE

δ/ppm F^(a) −114.2 F^(b) −121.6 F^(c) −135.2 F^(d) −83.5 F^(e) −143.3F^(f) −78.9 F^(g) −144.4 F^(h) −52.8

(n = 3)MPr₃VE

δ/ppm F^(a) −114.2 F^(b) −121.6 F^(c) −135.3 F^(d) −83.5 F^(e) −143.2F^(f) −78.9 F^(g) −144.5 F^(h) −52.9

(n = 4)MPr₄VE

δ/ppm F^(a) −114.2 F^(b) −121.6 F^(c) −135.3 F^(d) −83.4 F^(e) −143.1F^(f) −78.8 F^(g) −144.5 F^(h) −52.9

(n = 5)MPr₅VE

δ/ppm F^(a) −114.1 F^(b) −121.7 F^(c) −135.3 F^(d) −83.5 F^(e) −143.1F^(f) −78.9 F^(g) −144.5 F^(h) −52.9

(n = 6)MPr₆VE

δ/ppm F^(a) −114.1 F^(b) −121.6 F^(c) −135.3 F^(d) −83.5 F^(e) −143.1F^(f) −78.8 F^(g) −144.5 F^(h) −52.9

Reference Example 2

36 g of cesium fluoride, 360 g of diglyme, and 4.5 kg ofCF₃CF₂OCF(CF₃)COF were charged into a stainless steel autoclave having acapacity of 10 L, provided with a stirrer, stirred overnight, and thencooled to −10° C., and 12.0 kg of hexafluoropropene oxide was addedthereto at a feed rate of 150 g/hr. After the end of addition, themixture was further stirred for 2 hours, while keeping that temperature,and then returned to room temperature. Then, stirring was discontinued,and the mixture was allowed to stand. Then, only the fluorocarbon phasewas carefully withdrawn from the lower outlet of the autoclave. 11.8 kgof the fluorocarbon phase thus obtained was analyzed by gaschromatography (GC), and found to have the following composition:

CF₃CF₂O[CF(CF₃)CF₂O]nCF(CF₃)COF n GC (%) 2 2 3 28 4 51 5 17 6 2

1.3 kg of the resulting fluorocarbon phase, and 1.3 kg of anhydrouspotassium carbonate were charged into a glass reactor vessel having acapacity of 10 L, provided with a stirrer, and heated to 130° C. Aftercompletion of carbon dioxide gas generation, the vessel inside pressurewas reduced to 1 Torr to recover unreacted fluorocarbon mixture and avery small amount of diglyme (total: 42 g). Then, the vessel insidepressure was returned to the normal pressure, and reaction was conductedat 200°-270° C. for 10 hours to obtain the following compounds. Theresulting liquid was recovered by a cold trap. 1.0 kg of the resultingproduct was analyzed by GC, and found to have the following composition.Vinylation reaction proceeded substantially quantitatively (90% ormore), and thus the composition was not changed substantially before andafter the reaction.

CF₂═CFO[CF₂CF(CF₃)O]nCF₂CF₃ n GC (%) 2 2 3 29 4 52 5 16 6 1

The resulting vinyl ether compounds were distilled to isolate theindividual compounds having the respective n values from one another.The individual compounds were identified by ¹⁹F-NMR (chemical shift wasbased on CFCl₃).

(n = 2)EPr₂VE

δ/ppm F^(a) −114.2 F^(b) −121.6 F^(c) −135.1 F^(d) −83.5 F^(e) −143.4F^(f) −78.9 F^(g) −144.4 F^(h) −53.0 F^(i) −86.9

(n = 3)EPr₃VE

δ/ppm F^(a) −114.2 F^(b) −121.6 F^(c) −135.2 F^(d) −83.5 F^(e) −143.4F^(f) −78.9 F^(g) −144.4 F^(h) −53.0 F^(i) −86.9

(n = 4)EPr₄VE

δ/ppm F^(a) −114.1 F^(b) −121.5 F^(c) −135.2 F^(d) −83.6 F^(e) −143.3F^(f) −78.9 F^(g) −144.4 F^(h) −52.9 F^(i) −86.9

(n = 5)EPr₅VE

δ/ppm F^(a) −114.1 F^(b) −121.5 F^(c) −135.2 F^(d) −83.6 F^(e) −143.2F^(f) −78.8 F^(g) −144.2 F^(h) −52.8 F^(i) −87.0

(n = 6)EPr₆VE

δ/ppm F^(a) −114.2 F^(b) −121.4 F^(c) −135.1 F^(d) −83.4 F^(e) −143.2F^(f) −78.8 F^(g) −144.2 F^(h) −52.8 F^(i) −87.0

Example 1

A stainless steel autoclave having a capacity of 500 ml was internallyflushed with a nitrogen gas, and after the deaeration the followingreaction medium were charged thereto:

Surfactant CF₃CF₂CF₂OCF(CF₃)CF₂OCF(CF₃)COONH₄ 30 g Na₂HPO₄•12H₂O 0.5 gIon-exchanged water 250 ml

The autoclave was again internally flushed with a nitrogen gas, andafter the deaeration the following reactant materials were chargedthereto.

Vinylidene fluoride [VdF] 42 g Perfluoro (methyl vinyl ether) [FMVE] 28g CF₂═CFO[CF₂CF(CF₃)O]₄CF₃ [MPr₄VE] 39 g CF₂═CFO[CF₂CF(CF₃)O]₄CF₂CF₃[EPr₄VE]  5 g CF₂═CFOCF₂CF₂Br [FBrVE]  2 g ICF₂CF₂CF₂CF₂I [DIOFB] 0.5 g 

Then, the autoclave inside temperature was adjusted to 50° C., and 0.01g of sodium hydrogen sulfite and 0.05 g of ammonium persulfate wereadded thereto each as an aqueous 0.3 wt. % solution to initiatepolymerization reaction. After the reaction for 2 hours, the autoclavewas cooled, and the residual gas was vented therefrom, and the resultingemulsion was taken therefrom, and admixed with an aqueous 5 wt. %calcium chloride solution to coagulate the polymer. By water washing anddrying, 110 g of elastomeric copolymer (ηsp/c=0.41, Tg=−38.7° C.) havingthe following composition (by ¹⁹F-NMR method) was obtained.

VdF  78 mol. % FMVE  17 mol. % MPr₄VE 3.7 mol. % EPr₄VE 0.5 mol. % FBrVE0.8 mol. %

The following compounds were added to 100 parts by weight of theelastomeric copolymer:

Parts by weight MT carbon black (Thermax N990, a product of 30 CancabCo.) Triallyl isocyanurate (TAIC M60, a product of 6 Nihon Kasei Co.)Organic peroxide (Perhexa 25B-40, a product of 1.4 NOF Corp.) ZnO 4The mixture was kneaded through a two-roll mill, and the resultingcurable composition was compression molded at 180° C. for 10 minutes toobtain 2 mm-thick sheets and O rings (P24), and further subjected tosecondary vulcanization (oven vulcanization) at 200° C. for 10 hours.

The following tests were conducted at the time of vulcanization and alsoto the resulting vulcanizates:

-   -   Hardness test: To determine t₁₀, t₉₀, ML and MH values at 180°        C., using a Monsanto disc rheometer    -   Normal state physical properties: according to JIS K6251 and        6253, corresponding to ASTM D412    -   Elongation at heating: according to JIS K6251, corresponding to        ASTM D412 (at 100° C.)    -   Compression set: To determine 200° C., 30° C. or 0° C./70 hrs        values of P24 O rings according to ASTM D395 Method B    -   Low-temperature characteristics: To determine TR₁₀ and TR₇₀        values according to ASTM D1329    -   Methanol swelling test: To determine percent volume change after        dipping in methanol at 25° C. for 70 hours

Example 2 and Comparative Examples 1 to 3

In Example 1, the reactant materials were changed as given in thefollowing Table 1, where yields of the resulting elastomeric copolymers,copolymer compositions (sum total of MPr₄VE and EPr₄VE: 4.2 mol. %),solution viscosities ηsp/c, and glass transition temperatures Tg (bySEIKO I SSC5200) are shown together.

TABLE 1 Comp. Determination item Ex. 2 Comp. Ex. 1 Ex. 2 Comp. Ex. 3[Reactant Materials] VdF (g) 42 42 42 42 FMVE (g) 28 28 28 28 MPr₄VE (g)34 44 16 — EPr₄VE (g) 10 — 28 44 FBrVE (g) 2 2 2 2 DIOFB (g) 0.5 0.5 0.50.5 [Copolymer yield] Yield (g) 107 111 108 108 [Copolymer Composition]VdF (mol. %) 78 78 78 78 FMVE (mol. %) 17 17 17 17 MPr₄VE (mol. %) 3.24.2 1.5 — EPr₄VE (mol. %) 1 — 2.7 4.2 FBrVE (mol. %) 0.8 0.8 0.8 0.8[Solution Viscosity] η sp/c (dl/g) 0.43 0.41 0.46 0.48 [Glass TransitionTemperature] Tg (° C.) −38.8 −38.6 −39.1 −39.3

Curable compositions were prepared from elastomeric copolymers obtainedin Example 2, and Comparative Examples 1 to 3, and vulcanized, in thesame manner as in Example 1, and results of determination in the tests,conducted at the time of vulcanization and to the vulcanizates, areshown in the following Table 2, together with results of determinationin Example 1.

TABLE 2 Comp. Comp. Comp. Determination item Ex. 1 Ex. 2 Ex. 1 Ex. 2 Ex.3 [Curing test] t₁₀ (min.) 0.5 0.5 0.5 0.5 0.6 t₉₀ (min.) 1.7 1.7 1.71.8 1.9 ML (dN · m) 0.5 0.4 0.4 0.4 0.4 MH (dN · m) 10.3 10.5 10.0 10.510.3 [Normal state physical properties] Hardness 67 67 67 68 68 100%modulus (MPa) 5.5 5.8 5.8 5.6 5.7 Strength at break (MPa) 11.3 11.5 11.811.9 11.1 Elongation at (%) 160 160 160 150 150 break [Elongation atheating] 100° C. (%) 140 140 140 100 100 [Compression set] 200° C. for70 (%) 31 32 31 34 35 hours 30° C. for 70 (%) 40 41 46 42 42 hours 0° C.for 70 hours (%) 52 53 63 52 50 [Low-temperature characteristics] TR₁₀(° C.) −37.1 −37.1 −36.9 −37.1 −37.2 TR₇₀ (° C.) −26.4 −26.5 −26.4 −26.6−26.8 [Methanol swelling test] Percent volume (%) +32 +32 +32 +34 +33change

It is evident from the results shown in Table 2 that the vulcanizates ofthe present fluorine-containing elastomers have distinguished values inthe elongation at break at high temperatures such as 100° C. andcompression set characteristics at low temperatures such as 0° C.,whereas Comparative Example 1 using no EPr₄VE can satisfy the value ofelongation at break at high temperatures but has a poor value ofcompression set at low temperatures, and Comparative Example 2 usingmore EPr₄VE than MPr₄VE and Comparative Example 3 using no MPr₄VE cansatisfy values of compression set at low temperatures, but have poorvalues of elongation at break at high temperatures.

1. A fluorine-containing elastomer having a copolymer composition, whichcomprises the following Components: (a) vinylidene fluoride 50-85 mol.%  (b) tetrafluoroethylene 0-25 mol. % (c) perfluoro(methyl vinyl ether)7-20 mol. % (d) CF₂═CFO[CF₂CF(CF₃)O]nCF₃ 2.5-15 mol. %   (where n isanis an integer of 2-6) (e) CF₂═CFO[CF₂CF(CF₃)O]mCF₂CF₃ 0.1-2 mol. % (where m isan is an integer of 2-6) (f) RfX (Rf is an unsaturatedfluorohydrocarbon 0.1-2 mol. %  group having 2-8 carbon atoms, which cancontain at least one ether bond, and X is bromine or iodine)


2. A fluorine-containing elastomer according to claim 1, wherein inComponent (d), n is 4-6.
 3. A fluorine-containing elastomer according toclaim 1, wherein in Component (e), m is 4-6.
 4. A fluorine-containingelastomer according to claim 1, wherein in Component (d), n is 4, and inComponent (e), m is 4, respectively.
 5. A fluorine-containing elastomeraccording to claim 1, which has a solution viscosity ηsp/c (35° C., 1wt. % methyl ethyl ketone solution) of 0.1-2 dl/g.
 6. Afluorine-containing elastomer according to claim 1, which is obtained bycopolymerization reaction in the presence of a bromine- and/oriodine-containing compound, represented by the following generalformula:R(Br)n(I)m (where R is a saturated fluorohydrocarbon group, or saturatedchlorofluorohydrocarbon group, each having 2-6 carbon atoms, and m and nare each 0, 1 or 2, and m+n is 2).
 7. A fluorine-containing elastomeraccording to claim 1, which has a glass transition temperature Tg of−30° to −45° C.
 8. A fluorine-containing elastomer according to claim 1,wherein a sum total of Component (c), Component (d), and Component (e)is 10 mol. % or more.
 9. A fluorine-containing elastomer according toclaim 1, wherein the compound of Component (f) is CF₂═CFOCF₂CF₂Br,CF₂═CFBr, CF₂═CHBr, CF₂═CFI or CF₂═CHI.
 10. A fluorine-containingelastomer according to claim 6, wherein the bromine- and/oriodine-containing compound is ICF₂CF₂CF₂CF₂I.
 11. A fluorine-containingelastomer according to claim 1, which is capable of giving vulcanizatesshowing low-temperature characteristics (according to ASTM D1329), as:−34° C.≦TR10<−30° C.<TR70≦−20° C. after organic peroxide cross-linking.12. A fluorine-containing elastomer composition, which comprises 100parts by weight of a fluorine-containing elastomer according to claim 1,0.1-10 parts by weight of an organic peroxide, 0.1-10 parts by weight ofa polyfunctional unsaturated compound, and at least 2 parts by weight ofan acid acceptor.
 13. A fluororubber-based seal material, which isobtained by cross-linking molding of a fluorine-containing elastomercomposition according to claim
 12. 14. An automobile fuel seal materialwhich comprises a fluororubber-based seal material according to claim13.